CYTOSOLIC PH VARIATIONS IN PERFUSED-RAT-LIVER AT 4-DEGREES-C - ROLE OF INTRACELLULAR BUFFERING POWER

The effect of low temperature on cytosolic pH regulation and buffering capacity was evaluated in the isolated rat liver. The pH changes were followed by phosphorus-31 nuclear magnetic resonance. Cooling from 37 to 4 degrees C, with Krebs-Heinseleit perfusion at an external pH of 7.35, induced an alkaline shift in cytosolic pH (pH(cyt)) of 0.13 or 0 .75 pH units in the presence or absence of bicarbonate, respectively ( dpH(cyt)/dT values were 0.004 and 0.022 unit/degrees C). With 4 degree s C perfusion, in the presence or absence of bicarbonate, acute change s of external pH (from 7.40 to 5.90) did not affect pH(cyt). In contra st, intracellular loading with isobutyric acid or NH4Cl induced rapid pH(cyt) variations. The intrinsic buffering power value (10 to 50 slyk es) measured in the absence of bicarbonate depended on pH(cyt). The la rger value was observed for pH(cyt) 7.30, a value near the pK value of the imidazole group of intracellular proteins at 4 degrees C. The pre sence of bicarbonate modified the amplitude of the pH(cyt) change by i ncreasing the total buffering power. It was demonstrated that during h ypothermia, ionic carriers are inactivated and the charged forms of mo lecules are unable to cross the cell membrane; thus, the pH(cyt) meost asis depends essentially on intracellular buffering power, (C) 1998 Ac ademic Press.